Is there a formula—some mix of love, work, and psychological adaptation—for a good life? For 72 years, researchers at Harvard have been examining this question, following 268 men who entered college in the late 1930s through war, career, marriage and divorce, parenthood and grandparenthood, and old age. Here, for the first time, a journalist gains access to the archive of one of the most comprehensive longitudinal studies in history. Its contents, as much literature as science, offer profound insight into the human condition—and into the brilliant, complex mind of the study’s longtime director, George Vaillant.

Do you know someone who needs hours alone every day? Who loves quiet conversations about feelings or ideas, and can give a dynamite presentation to a big audience, but seems awkward in groups and maladroit at small talk? Who has to be dragged to parties and then needs the rest of the day to recuperate? Who growls or scowls or grunts or winces when accosted with pleasantries by people who are just trying to be nice?

If so, do you tell this person he is "too serious," or ask if he is okay? Regard him as aloof, arrogant, rude? Redouble your efforts to draw him out?

If you answered yes to these questions, chances are that you have an introvert on your hands—and that you aren't caring for him properly.